the settings UI is absolutely awful;

depending on which appearance you choose, it either looks ugly or blurs together;

it frequently has visual glitches;

could certainly be more customisable appearance and shortcut-wise;

doesn’t allow you to have a title or marker as the top level tab;

as far as I can tell doesn’t let you save a session of tabs;

has an unpleasant glitch where if you drop a tab in the wrong place it’ll disappear behind the current window and never be reachable;

the new tab behaviour irritates me;

and probably a few more complaints that I’d have to actually open it up to remember

They do strip Google crud like FLoC, don’t pander to crypto scams and are employee-owned, you can check out their statements on Vivaldi.com. The only valid reason not to consider them would be that they are not open-source.